The present invention relates to a small liquid crystal display device which is inserted in a projector for projecting an image on the liquid crystal display device onto a screen.
The liquid crystal display device used for the purpose of the projection of the image is classified into two large groups as follows.
(I) A liquid crystal projector having a light source, a lens for magnifying the image, and a liquid crystal display panel integrally assembled in the projector. PA1 (II) A projector having a light source and a lens for magnifying the image, in which a liquid crystal display device is detachably mounted. PA1 (II-1) An over head projector (OHP) on which a liquid crystal display device is mounted. PA1 (II-2) A slide projector in which a liquid crystal display device is inserted.
Further, the system of (II) is divided to two types.
The systems of groups (I) and (II-1) are produced and sold now.
Japanese Utility Model Application Laid-open Publications 61-119145 and 62-12147 disclose a system of group (II-2).
FIG. 7 shows a conventional liquid crystal display device disclosed in the Japanese Utility Model Application Laid-open Publication 61-119145. The device comprises a projector 600 in which a light source 603 and a plurality of lenses 601 are provided. A liquid crystal display panel module 606 is adapted to attach to the projector 600 and electrically connect thereto through a connector 607 of the module 606 and a connector 604 of the projector 600. The module 606 is illuminated by the light source 603 and an image of the module is magnified by lenses 601 and projected on a screen 601.
FIGS. 8a and 8b show another conventional device disclosed in the Japanese Utility Model Application Laid-open Publication 62-12147. A holder 706 is interposed between a light source 702 and a lens 704 in a projector 700. The holder 706 is adapted to hold a slide film 707 and a liquid crystal display plate 703. The holder 706 attached to the projector 700 is reciprocated in the horizontal direction as shown by arrows a and b in FIGS. 8a, so that either of the slide 707 and the plate 703 may be selected.
In the conventional projector, a tungsten halogen lamp is used for the light source. The light emitted from the light source includes the infrared ray having a wavelength of 770 nm or more. In particular, when the material of the liquid crystal display panel absorbs the light including a near infrared ray having a wavelength of 50 .mu.m or less, thermal motion occurs in the material so that the temperature of the material rises. The projector is usually provided with a heat absorbing filter to shut off the near infrared ray. However, it is difficult to completely absorb the near infrared ray with the heat absorbing filter. When it is intended to increase the magnification of the image so as to provide a bright image on the screen, a light source having a large illuminance must be used. However, quantity of heat in the material increases. If the temperature of the liquid crystal exceeds a predetermined value which is determined in accordance with the material of the liquid crystal, the liquid crystal becomes isotropic, so that no image appears on the display panel. Therefore, it is necessary to take measures for heat. Furthermore, in the case that high contrast of the image is required, polarized plates are provided in the liquid crystal display device. However, the polarized plates absorb about 50% of the transmitted light the energy of which becomes heat. If the polarized plates are attached to glasses forming the liquid crystal display panel, the temperature of the liquid crystal between glasses rises.
In conventional liquid crystal display systems described above, neither the liquid crystal display panel module 606 shown in FIG. 7 nor holders 706 and liquid crystal display plate 703 shown in FIG. 8 are provided with any structures to avoid rise of the temperature of the liquid crystal.